Mysterious descending/battery issue

I have two phantom II setups that I use for aerial real estate photography and they both have started to have this same malfunction. I will take off and moments... to less than 5 minutes later I will get flashing red lights on the copter and it will descend straight down where it is... as if the battery is dead. This happens, however, when I have 3, sometimes, 4 green battery level indicator lights. I have two batteries and have tried both. My setup includes the Go Pro and Fat Shark Predator FPV transmitter. Any suggestions? I'm loosing work. Thanks!!